Principal Proposed Uses

Other Proposed Uses

Bladderwrack is a type of seaweed found on the coasts of the North Sea, the western Baltic Sea, and the Atlantic and Pacific Oceans. A common food in Japan, it is used as an additive and flavoring in various food products in Europe. Bladderwrack is commonly found as a component of
kelp
tablets or powders used as nutritional supplements. It is sometimes loosely called kelp, but that term technically refers to a different seaweed.

What Is Bladderwrack Used for Today?

Bladderwrack contains high concentrations of
iodine
, and for this reason it has been recommended as a treatment for
hypothyroidism
(underactive thyroid gland).
1
However, iodine will only help for the type of hypothyroidism caused by iodine deficiency, which is a relatively rare condition in the developed world. If your iodine levels are not low, taking extra amounts of iodine can cause your thyroid gland to become either over- or underactive,
causinghyperthyroidism
or hypothyroidism, respectively. Furthermore, the amount of iodine supplied by bladderwrack is unpredictable.

A component of bladderwrack called alginic acid swells upon contact with water. When taken orally, it forms a type of seal at the top of the stomach, and for this reason is used in over-the-counter preparations for
heartburn
. The same constituent gives bladderwrack laxative properties, as well.
2

Dosage

It is important not to take bladderwrack in dosages providing more than the recommended daily intake of iodine. For more information on the appropriate intake for various groups of people, see the
iodine
article. Products that provide bladderwrack should state the amount of iodine they provide. If this information is not there, do not take it.

Safety Issues

Studies have found that levels of iodine vary widely among bladderwrack products.
5
Because of this, if you use bladderwrack as a regular supplement, there is a real risk you may receive an overdose of iodine and develop
hyperthyroidism
or
hypothyroidism
.

Bladderwrack and other seaweed preparations can also worsen
acne
and decrease
iron
absorption.
6

Finally, bladderwrack, like other sea plants, can concentrate toxic heavy metals, such as arsenic, from the surrounding sea water.
7
One report suggests that use of a bladderwrack product with a high heavy metal content is responsible for a case of kidney failure.
9
Heavy metals present particular risks for pregnant or nursing women, children, individuals with kidney disease, or anyone using bladderwrack in high doses or over a long period of time.

Revision Information

This content is reviewed regularly and is updated when new and relevant evidence is made available. This information is neither intended nor implied to be a substitute for professional medical advice. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with questions regarding a medical condition.